Re: Opinion on timing system for synchrotron beamlines

[Márcio Paduan Donadio <marcio.donadio@lnls.br>]

        Hello, Bob.

    We are in the project phase of Sirius' beamlines control system. We did the requirements gathering with the researchers and no one cited the synchronization with the accelerator timing system, with one exception: the pump and probe experiments. So it seemed that it was a special case.

    But some time ago I was evaluating a Zebra Box and asked a friend that works with beamlines in the USA to comment about his impressions on this system. Among some things he told me that Zebra Box lacks from direct connection with the EVG and that is an important feature because he needed to get the global timestamp from it.

    So, I thought that, maybe, we don't know yet that we will need to synchronize events during some other experiments like quick exafs, fly scan mapping, and tomography. That's why I'm talking to you guys, that have more experience on beamline's timing system.

    Thank you very much,

-- 
Márcio Paduan Donadio
Engenheiro de Computação - Software de Operação das Linhas de Luz
Laboratório Nacional de Luz Síncrotron – (LNLS)
Centro Nacional de Pesquisa em Energia e Materiais (CNPEM)
+ 55 (19) 3512-3520 - marcio.donadio@lnls.br
www.lnls.cnpem.br

Em 09-11-2016 17:52, bob dalesio escreveu:

First a disclaimer: The actual EPICS developers always have a better answer about the technology as is. 

That said, I will take a shot at it:

Hi Marcio,

This is really a question that starts at the beam line.

What do they want? Do they care about the energy? at what precision?

There are independent timing systems implemented in FPGAs with different specifications. If you cannot buy hardware, working with this firmware allows you to build your own.

EPICS time stamps can be derived from different timing sources. If you use PTP, as I understand it, you have to purchase a master as well (is that right?). So, it is important to know what your beam lines want and your cost constraints.

EPICS itself in version 3 has time to the nsec. The MRF timing hardware time stamp resolution is 8 nsec. The jitter is < 10 psec. It can easily be extended to the beam lines. Slow signals, like beam energy, can be sent over the timing system along with time stamp information that could be put into the metadata for the experiment. LCLS II timing has sub nsec time derived at the EVR from the EVG (both homemade at SLAC). PVAccess has 64 bits for subsecond instead of 32 bits. It also has a user defined extension for pulse ID or other user defined identifier.

- Bob

On Wed, Nov 9, 2016 at 2:26 PM, Márcio Paduan Donadio <marcio.donadio@lnls.br> wrote:

     I'd like to know your experience regarding integration of the
accelerator timing system with the beamlines:
     - Which accelerator events are useful for the beamlines' control
system.
     - Do the beamlines use a global and very precise timestamp sent
from the accelerator timing system? What is the time precision?
     - Do you think that a PTP system is sufficient for timestamping
experiments in beamlines?
     - What is the EPICS role regarding such a timing system?

     Thank you,

--
Márcio Paduan Donadio
Engenheiro de Computação - Software de Operação das Linhas de Luz
Laboratório Nacional de Luz Síncrotron – (LNLS)
Centro Nacional de Pesquisa em Energia e Materiais (CNPEM)
+ 55 (19) 3512-3520 - marcio.donadio@lnls.br
www.lnls.cnpem.br